Pogonura, Komeda & Ohtsuka, 2020

Komeda, Sota & Ohtsuka, Susumu, 2020, New genus and species of calanoid copepods (Crustacea) belonging to the group of Bradfordian families collected from the hyperbenthic layers off Japan, ZooKeys 951, pp. 21-35 : 21

Genus Pogonura gen. nov.

Diagnosis.

Female. Body compact. Cephalosome incompletely fused to first pediger with suture line dorsally and laterally visible. Fourth and fifth pedigers completely fused, weakly produced posteriorly into round lobes. Rostrum produced ventrally, with pair of filaments. Genital double-somite symmetrical, with pair of seminal copulatory pores and seminal receptacles; seminal copulatory pores ovaliform; genital operculum ventrally located midway; two spiniform setae located ventrolaterally, as long as genital double-somite. Antennule 24-segmented, with ancestral segments II-IV, X-XI, and XXVII-XXVIII fused; II-IV, VII, X-XI, XIV, XVI, XXI and XXVII-XXVIII with aesthetasc. Setal formula of antennary exopod as follows: 1, 1-1-1, 1, 1-1, 1, 0, 3. Mandible with gnathobase having 1 triangular ventral tooth, 5 chitinized teeth, 16 long setules, and 1 dorsal seta. Maxillulary exopod with 8 setae. Maxillary endopod with 5 brush-like setae and 3 sclerotized setae. Maxilliped with syncoxa having 1, 2, 3, 3 sclerotized setae. Legs 1-4 of typical clausocalanoidean segmentation and setation. Posterior surface of legs 2 and 3 with an exopodal spinule and 3 endopodal spinules. Leg 5 uniramous, 2-segmented, distal segment with 3 lateral process and 1 articulated spine.

Male. Body similar to that of female. Fusion between cephalosome and first pediger and between fourth and fifth pedigers resembling those of female. Genital somite with gonopore on left side. Rostrum as in female. Right antennule 22-segmented, with ancestral segments II-IV, X-XII, XXII-XXIII, and XXVII-XXVIII fused. Left antennule 23-segmented, with ancestral segments II-IV, X-XII, and XXVII-XXVIII fused. Antenna, mandible, maxillule, maxilla, maxilliped and legs 1-4 similar to those of female. Leg 5 complex in structure. Right leg uniramous, endopod absent; expod 2-segmented. Left leg biramous with 1-segmented endopod; exopods 2-segmented, decorated by various armatures; distal part of exopod with rugose plate.

Remarks.

Because Pogonura gen. nov. has brush-like sensory setae on the maxillary endopod, it can be assigned to one of the Bradfordian families. The new genus can be tentatively included in Diaixidae because it fits the familial diagnosis proposed by Markhaseva et al. (2014), except for the proximal basal endite of the maxillule with 3 setae (vs. 4 setae typical for the Diaixidae ) and 2-segmented exopods of both legs 5 of the male.

The present new genus also shares the following characteristics with the diaixid genus Procenognatha ( Markhaseva and Schulz 2010): the maxilliped carries no specialized sensory setae; legs 2 and 3 carry 3 large spinules on the posterior surface; and leg 5 of the female is uniramous, 2-segmented, with the distal segment having 3 processes and 1 articulated spine.

The male of the present new species has complex structures on leg 5, which can be seen in other diaixid genera such as Anawekia and Diaixis . These three genera have rows of setules and/or spinules on the left exopod of leg 5 [cf. figs 7 and 9 in Othman and Greenwood (1994); figs 11 and 12 in Andronov (1979)], and these setulae and/or spinules seem to be homologues in position and shape. However, Anawekia and Diaixis have some derivative characteristics: (1) the posterior corner of the prosome, leg 4, and the urosome of both sexes are asymmetrical; (2) female leg 5 is totally reduced; and (3) the left endopod of male leg 5 is reduced.

According to Markhaseva et al. (2014), the family Diaixidae has hitherto accommodated 15 genera. Pogonura gen. nov. is differentiated from these diaixid genera by the following features (morphological data from Markhaseva et al. 2014): (1) the genital double-somite of the female has a symmetrical pair of long spiniform setae (only Pogonura gen. nov.), (2) the distal part of the left exopod on male leg 5 has a rugose plate (only Pogonura gen. nov.), (3) the ancestral segments XI-XII of the male antennule are fused (shared by Pogonura gen. nov., Byrathis , Diaixis , Paraxantharus , Procenognatha and Xantharus ), (4) the setal formula of the antennary exopod is 1, 1-1-1, 1, 1-1, 1, 0, 3 (only Pogonura gen. nov.), (5) the mandibular gnathobase has long setules ( Pogonura gen. nov., Cenognatha , Neoscolecithrix , Paraxantharus and Procenognatha ), and (6) the maxillary endopod has 3 sclerotized setae ( Pogonura gen. nov. and Procenognatha ).

Etymology.

The new generic name is derived from two Greek words pogon, meaning “beard”, and oura, meaning “tail”, to denote the paired setae like moustache on the genital double-somite of the female. Gender feminine.

Type species.

Pogonura rugosa sp. nov. (original designation).